1. Field of the Invention
Apparatuses and methods consistent with the exemplary embodiments relate to a power supply apparatus, a power supply system and a method of supplying power thereof, and more particularly, to a power supply apparatus, a power supply system and a method of supplying power thereof, in which sunlight is absorbed and converted into electric power, thereby supplying power.
2. Description of the Related Art
A conventional converter that converts electric power output from a solar cell of absorbing sunlight employs a control method for reducing a charging current in accordance with input power from the solar cell through maximum power point tracking (MPPT), so that power conversion can be performed by keeping the maximum available value, i.e., the maximum voltage of the output power from the solar cell. In a conventional MPPT, a maximum output occurs when a source resistance of the solar cell equals a load resistance of a load realized by the solar cell.
FIG. 1 is a graph showing power conversion based on the MPPT control, in which a dotted line indicates an electric current output from the solar cell and a solid line indicates an output voltage of the solar cell. Since power is the product of voltage and current, it is possible to find out the maximum power in an “A” line. Thus, it will be appreciated that current is decreased at a constant voltage Voc (open circuit voltage) when tracking a point of current decreased in accordance with incident energy of the solar cell. The MPPT control is a method of controlling the power to be always output at a maximum power point by measuring current and voltage at an output terminal of the solar cell, receiving the values of the measured current and voltage through an analog-digital converter (ADC), decreasing a duty ratio of the converter if the measured current and voltage are lower than the maximum power point, and increasing the duty ratio of the converter if the measured current and voltage are higher than the maximum power point.
However, if the incident energy to the solar cell is rapidly varied with rapid variation of sunshine, the conventional converter employing the MPPT control has to rapidly decrease/increase the duty ratio in order to output power at the maximum power point in accordance with the rapid variation of the incident energy. At this time, the converter is under undue electrical stress, and noise occurs due to voltage variation at an input terminal of the converter.
To reduce the electrical stress on the converter due to rapid variation in the incident solar energy, an energy storage tank such as a lithium ion battery may be provided at the input terminal of the converter. However, if the incident solar energy exceeds the capacity of the energy storage tank, the same problem may arise as described above. Further, there is a shortcoming in that the energy storage tank is expensive.
Also, there is a problem in that the conventional converter based on the MPPT control does not take into account any load variation.